SL/R230: Does charging the rear battery also charge the front ?
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Junior Member
Joined: Apr 2022
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Sl600
Does charging the rear battery also charge the front ?
Good morning and Happy Holidays. Can anyone confirm if changing the “Consumer” battery in the trunk,with a trickle charger also charges the front batter too? Thank you
Senior Member
Joined: Nov 2010
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From: Norway
350 SL, R230 - 300 SL, R129 - 1964 Corvette Sting Ray Sport Coupe - Porsche 911 Twin Turbo (sold)
If you charge the battery in the trunk i am pretty sure that you do not charge the battery in the engine compartment
So if you want to charge both batteries at the same time over a long period of time i guess you will need 2 trickle chargers
I use a trickle charger on the battery in the trunk (the car is not being used during the cold and snowy winters we have here in northern Europe)
I never had to charge the battery in the engine compartment
So if you want to charge both batteries at the same time over a long period of time i guess you will need 2 trickle chargers
I use a trickle charger on the battery in the trunk (the car is not being used during the cold and snowy winters we have here in northern Europe)
I never had to charge the battery in the engine compartment
Last edited by TheSaint; Apr 16, 2022 at 12:40 PM.
MBWorld Fanatic!
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95 SL600
I do not believe this is correct, I have both batteries out of my car and tested continuity between front and rear positive leads. There is none when no batteries are connected. This could change when power is connected to them, but I believe except for emergency operation they are separated.
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Joined: Nov 2021
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From: North West England
SL500
I do not believe this is correct, I have both batteries out of my car and tested continuity between front and rear positive leads. There is none when no batteries are connected. This could change when power is connected to them, but I believe except for emergency operation they are separated.
Both batteries are connected to the BCM.
Inside the BCM is a DC to DC converter (circuit that takes one DC voltage and converts it to another DC voltage, usually higher). This is effectively a battery charger powered by the consumer battery that charges the starter battery. This is the only way the starter battery gets charged (exception below).
The consumer battery is charged directly by the alternator, in a conventional way.
The only other thing that is connected to the starter battery is the starter motor, via the solenoid. This is why the starter battery does not normally discharge, unless cranking the engine as there is no parasitic drain on it.
The BCM controls the charge to the starter battery (it monitors the voltage on both batteries constantly), and will stop charging it if the consumer battery is too low.
Everything above assumes everything is working correctly.
Under certain conditions the two batteries are connected directly together (emergency mode) and they will for a short period act as a single larger battery (usually to start the engine if starter battery is a little low), in which case the starter battery will receive a direct charge from the alternator for a short time, but that is not normal operation.
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Senior Member
Joined: Nov 2010
Posts: 382
Likes: 27
From: Norway
350 SL, R230 - 300 SL, R129 - 1964 Corvette Sting Ray Sport Coupe - Porsche 911 Twin Turbo (sold)
I was 99,99 percent sure that if you charged the battery in the trunk there was no way you could charge the battery in engine compartment at the same time.
I often use a trickle charger on the consumer battery in the trunk and never had to charge the battery in the engine compartment.. Now i know why i never had to charge the battery in the engine compartment
I will have to read the PDF file because i really have no idea on how this is working
I often use a trickle charger on the consumer battery in the trunk and never had to charge the battery in the engine compartment.. Now i know why i never had to charge the battery in the engine compartment
I will have to read the PDF file because i really have no idea on how this is working
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Joined: Oct 2021
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
You shouldn't find things to worry where there is no reason to worry about it..! Otherwise we may call you the Worries man! Just sit on it, find a good road and put the pedal to the metal! Don't worry that you may be hit by a meteor, or lightening......life is full of dangers and if you worry about all them, you won't be living a life!
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Joined: Jun 2020
Posts: 449
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From: Melbourne Florida
SL500
You shouldn't find things to worry where there is no reason to worry about it..! Otherwise we may call you the Worries man! Just sit on it, find a good road and put the pedal to the metal! Don't worry that you may be hit by a meteor, or lightening......life is full of dangers and if you worry about all them, you won't be living a life!
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Joined: Sep 2007
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95 SL600
It’s definitely happened more than once. There was an episode on the TV show Junkyard Empire where an r230 was purchased with the same trunk fire.
Not sure what actually causes it, but I do know it doesn’t make me feel good about the cars I have. The other issues with the car are quite a nuisance, but this particular one, even if it is rare is taking it to another level.
Not sure what actually causes it, but I do know it doesn’t make me feel good about the cars I have. The other issues with the car are quite a nuisance, but this particular one, even if it is rare is taking it to another level.
Senior Member
Joined: Oct 2021
Posts: 493
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Guys, I wasn't aware of this frequent incidence! Then I better keep this ride out of the garage and away from the house..!
I am aware that many homes have a gas water heater in the garage, and a small fuel leak may spark a fire, but for the trunk battery to cause the fire it should need a heck of a short and sparks. If the battery does not breathe correctly may create an accumulation of Hydrogen gas in the trunk which will burst if it finds an spark!
My apologies for the victims.!
I am aware that many homes have a gas water heater in the garage, and a small fuel leak may spark a fire, but for the trunk battery to cause the fire it should need a heck of a short and sparks. If the battery does not breathe correctly may create an accumulation of Hydrogen gas in the trunk which will burst if it finds an spark!
My apologies for the victims.!
Senior Member
Joined: Dec 2019
Posts: 407
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From: Houston, TX
2005 SL600
Guys, I wasn't aware of this frequent incidence! Then I better keep this ride out of the garage and away from the house..!
I am aware that many homes have a gas water heater in the garage, and a small fuel leak may spark a fire, but for the trunk battery to cause the fire it should need a heck of a short and sparks. If the battery does not breathe correctly may create an accumulation of Hydrogen gas in the trunk which will burst if it finds an spark!
My apologies for the victims.!
I am aware that many homes have a gas water heater in the garage, and a small fuel leak may spark a fire, but for the trunk battery to cause the fire it should need a heck of a short and sparks. If the battery does not breathe correctly may create an accumulation of Hydrogen gas in the trunk which will burst if it finds an spark!
My apologies for the victims.!
As far as the consumer battery and hydrogen gas - this is exactly why it is advised to use an AGM battery in this location. AGM batteries do not produce hydrogen gas under normal conditions, so they are always recommended for enclosed locations. They can still produce hydrogen gas if something in the charging system goes wrong and they are subjected to overcharging, so it's still a good idea to have a vent tube. There's already a grommeted hole right next to the consumer battery which lines up with a hole in the rear splash shield just for this purpose, so it's simple and cheap to install this safeguard.
All you're accomplishing with your snarky, sarcastic comments is
1) Showing that you're uninformed about known issues with the R230 and
2) Showing what kind of character you have.
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Joined: Mar 2018
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From: Netherlands
2005 R 230 SL350 (M112 3.7). Sold the 1966 W113 230SL recently
On one of the forums an (apparently) well informed electronics savvy made an educated guess, pinpointing a possible root of the potential BCM fire hazard. It made a lot of sense to me.
MBWorld Fanatic!
Joined: Mar 2018
Posts: 1,442
Likes: 260
From: Netherlands
2005 R 230 SL350 (M112 3.7). Sold the 1966 W113 230SL recently
Oh and let's always try to see the positive in comments folks make. I can't believe anyone is out to hurt or insult others.
